Author
Topic: CB750 camchain rattle? how to adjust? (Read 9844 times)

Tnrfd

- My cam chain rattles quite loud. I can hear it over the other engine noises when I cruise along. Is this normal or do the chain and tensioner need attention?

I have tride to adjust it, but ain't sure i got i right..

- How to adjust properly? the manual says TTC on cylinder #1 + 15degrees. Does this mean just piston #1 is on top (no mather if the valves are open or closed) or piston #1 on top AND both valves closed (start of the power stroke)??

First question above: "What is TDCC?" That's "Top Dead Center, Compression" stroke. The camchain should be set when cylinder #1 is 15 degrees past TDCC or #4 is passing TDC WHILE THE INTAKE VALVE IS STARTING TO OPEN, stopping in that forward direction at the "corner" of the spark advancer: that's the 15 degrees point. This geometry sets all the tension to the front side of the chain at the highest mechanical load point on the chain. Don't let the crank back off from here: release the tensioner's bolt, make sure the plunger moved inward (you can give it a tap with a small screwdriver and hammer to help), then tighten the little bolt and nut.

Logged

The demons are repulsed when a man does good. Use that.Blood is thicker than water, but motor oil is thicker yet...so, don't mess with my SOHC4, or I might have to hurt you.Hondaman's creed: "Bikers are family. Treat them accordingly."

At the risk of opening a can of worms, the easiest way to do it is the same as that recommended for a lot of cars.

Get someone to push the kickstart down gently, just so resistance is felt.

This pulls the chain in the direction of rotation & leaves any slack at the rear of the motor.

Undo the adjuster etc & you're done.

If I tension the cam chain using the kickstart method, do I need to turn the engine to Nr 1 TDCC?

While this sounds reasonable, I submit it will not absolutely result in a properly tensioned chain. If you loosen the tension bolt, then put a small screwdriver in the back of the tensioner you'll hit the end of the tensioner push bar. Now while you turn the engine over using the kickstart or the ignition nut, you'll feel the tensioner push bar go in and out A LOT. Some places have the slack on the back row, others have the slack on the front row. Depending on how the valve springs are pushing on the cam. Just because you are attempting to roll the engine forward does not guarantee slack in the back. If you just tighten the tensioner down at some random point, you could be locking all the slack in the front and it will be LOUD, or something in between.

This may be a characterisitic of the SOHC vs the car, but that's the way it works.

So the only way to be absoutelly sure you have ALL the slack at the optimum position is to use the #1 TDCC method +15°. And if you do, you'll be happy with the quiet sewing machine quality of the chain sound.

For other bikes, I've seen it recommended to stick something through the spark plug hole in nr 1 cylinder to determine TDCC- is there another, smarter way for The CB750?

And thanks for the help- I'm just not smart on this bike yet. Downloaded the manual today, going to start my homework now!

(1978 CB750F)

Remove the #1 intake valve tappet cover. Turn the engine forward and watch the tappet. It goes down, then starts back up. When it reaches the top of its travel, you will be very near TDCC. Continue forward to TDCC+15.